An electric arc furnace comprises a vessel having a refractory lining for containing a metal charge, and at least one arcing electrode extending down into the vessel with its bottom tip spaced above the charge to form an electrically powered arc which produces an arc flare which radiates against the refractory lining of the side wall of the vessel, causing premature erosion of the lining.
To shield the lining from the arc-flare, the U.S. Goodman Pat. No. 3,619,467, dated Nov. 9, 1971, discloses the use of an electromagnet on the outside of the lining and forming a flux field on the inside of the lining where the lining is normally exposed to the arc-flare. A flow of ferromagnetic particles is fed downwardly through this flux field so that the particles adhere to the lining and form a protective layer, the particles being held until, through heating, they become non-magnetic and fall, the feed of particles providing for their replacement and maintenance of the layer of protective particles. The electromagnet construction proposed has an iron core forming vertically interspaced pole pieces on which solenoid coils are coiled.
The effectiveness of the above proposal depends on the intensity of the flux field that can be created on the inside of the lining. To increase the strength of this flux field, the U.S. Hanas et al. U.S. Pat. No. 3,883,677, dated May 13, 1975, discloses an arc furnace construction wherein the furnace lining has its outer surface provided with a recess reducing the thickness of the lining so that the spacing between the external magnet and the lining's inside is reduced, means between the magnet and the recess for water-cooling the lining of reduced thickness being provided. In this case the magnet is also an electromagnet having vertically interspaced pole pieces on which solenoid coils are coiled.
Both patented furnaces involve a problem in that the layer of particles held on the inside of the furnace lining, is restricted as to its extent and is non-uniform in thickness, so that the protection provided by the layer of particles, is not as effective as is desirable.